1. Field of the Invention
This invention relates generally to polymer filtering equipment, and more particulary, to such equipment having structure to permit removal of seal material before it can enter the flow of filtered material leaving the equipment.
2. Description of the Prior Art
It is known in the art of filtering of polymers to employ one or more continuous filters passing through a heated, high pressure filtering chamber and to utilize at the filter entry and exit zones of such a chamber sealing plugs made of the substance being filtered. Such filtering equipment is shown, for example, in U.S. Pat. Nos. 3,471,017, 3,645,399, 3,856,674, 3,856,680 and 4,010,391.
The material forming the inlet seal in such filtering equipment eventually enters the filtering chamber and is ultimately incorporated into the product which is made from the filtrate. When materials are filtered which are sensitive to thermal history, this is disadvantageous in that the homogeneity of the product is affected since that part of the product which formed part of the seal will have undergone an added thermal cycle during the formation and the subsequent remelting of the seal. In addition, should a polymer color change be carried out during filtering (e.g. from black to clear transparent polymer) the previously formed inlet seal will have been made from the substance first filtered and will act as a contaminant when, during subsequent movements of the filter, the material comprising it is drawn into the filtering chamber then containing material of a different color.